This invention relates to a tensioners used with chain drives in automotive timing applications and more particularly to a blade-type tensioner which is provided mounted to a bracket and held in place by a retaining pin for shipping and convenient assembly to an engine.
Tensioning devices are used as a control device for a power transmission chain as the chain travels between a plurality of sprockets. Generally, it is important to impart and maintain a certain degree of tension to the chain to prevent noises or slippage. Prevention of slippage is especially important in the case of a chain driven camshaft in an internal combustion engine because slippage may alter the camshaft timing by several degrees, possibly causing damage. In the harsh environment in which an internal combustion engine operates, chain tension can vary between excessively high or low levels as a result of the wide variations in temperature and differences between the coefficients of linear expansion among the various parts of the engine, including the chain and the tensioner. Camshaft and crankshaft induced torsional vibration cause chain tension to vary considerably. This tension variation results in chain elongation. Moreover, wear of the chain components during prolonged use can cause elongation of the chain that results in a decrease in the tension of the chain.
Generally, blade-type tensioners use a spring blade interlocked under tension with a plastic shoe to provide tension to a chain. Before assembly into a operable tensioner the blade spring is preformed into an arcuate shape and the shoe is provided relatively flat. The shoe is constructed from a semi-rigid material which will deform or "creep" upon experiencing a load at high temperature. During assembly, the blade spring is flattened to correspond to the shape of the shoe and then interlocked with it. Because the semi-rigid shoe prevents the blade spring from returning to its original more arcuate shape, the blade spring applies a load to the shoe. After application of the tensioner to an engine, the heat from the engine, during operation, causes the temperature of the shoe to increase and become less rigid. The load from the blade spring causes the shoe to deform to a more arcuate shape. Through such deformation, tension is provided to a chain.
The chain tensioner is positioned to act against a free length of the chain between the sprocket gears. As the blade spring forces the shoe into a more arcuate shape, the apex of the shoe extends farther into the span of chain thereby increasing chain tension.
Typical blade-type chain tensioners have interlocked a blade spring to a shoe. For example, U.S. Pat. No. 3,490,302, to Turner et al., incorporated herein by reference, discloses a chain tensioner where the blade spring is mounted to mechanically interlock with, and thereby provide a load to, a shoe through a hole and pin combination. The blade spring continuously bears against the shoe.
Yet another structure for mounting a blade spring to a single shoe is disclosed in U.S. Pat. No. 5,055,088, to Cradduck et al., incorporated herein by reference. This reference discloses a blade-type tensioner which utilizes a plurality of blade springs interlocked with a plastic shoe through a passageway in the shoe and fastened using a split, or solid pin.
Unfortunately, the prior art blade-type tensioners have a drawback. Typically, blade-type tensioners are used in confined spaces and are supplied to engine assembly plants in a straight form for ease of assembly in the engine. In the prior art, the tensioner is fixed to a bracket in the flattened form by a retaining pin which passes between the blade spring and the shoe and engages a notch or slot formed in the shoe itself and further passes through a hole in the bracket fixing the blade tensioner in place. The formation of the notch in the shoe requires an additional manufacturing step and forms a potential weak spot in the shoe.
The prior art blade spring tensioner 10 is shown in FIGS. 1-3. The shoe 30 has a blade spring interconnected thereto, the blade spring including a pair of blade spring members 20, 22 disposed along a bottom face 21 of the shoe 30. One end of the blade spring is held by being inserted into a slot in the shoe. The other end of the blade spring has an opening 80 which is fitted over a projection 60 on the corresponding end of the shoe and is locked in place by a solid or split pin 50 passing crosswise through the projection 60.
A slot 70 is formed near the center of the bottom face 21 of the shoe 30 adapted to receive a retaining pin 55 (shown in FIG. 2). When the tensioner 10 is first mounted to the bracket 15, the retaining pin 55 is passed through the tab 25 formed on the bracket 15 aligned with the slot 70 in the center portion of the shoe 30 and through a hole formed in the bracket, thus locking the shoe in place.
FIG. 3 illustrates the prior art blade tensioner 10 as applied to a generalized power transmission system including a driving sprocket 81, a driven sprocket 82 and a chain 84 connecting the two sprockets. The blade tensioner 10 is mounted to the bracket 15 which, when mounted to the engine block 86, directs the upper face 23 of the tensioner shoe 30 to tension the slack portion of the chain 84. The bracket 15 includes a tab 25 spaced outward from the bracket face and located adjacent to the mid portion of the tensioner shoe 30. The bracket 15 further includes a passive snubber 88 generally opposite the tensioner 10 and applied to the drive side of the chain.
The present invention is directed to a blade tensioner that addresses the problem of retaining the tensioner to the bracket by supplying a ready-to-use assembly that is easy and inexpensive to manufacture, simple to apply to an engine and results in a stronger tensioner.